New dinosaurs appear to be oldest yet, as reported in the 22 October issue of Science

October 21, 1999

Washington DC - The jaws of two of the oldest dinosaurs ever discovered and the remains of eight other prehistoric animals have been unearthed by a team of paleontologists working in Madagascar. The exquisitely preserved collection of fossils provides a freeze-framed picture of life during the earliest days of dinosaurs and mammals--a picture that has been largely obscured until now. The team reports its find in the 22 October issue of Science.

The fossils are from a period that has long been a puzzle for paleontologists, the Middle to Late Triassic (225 to 230 million years ago). At the opening of this period, a variety of reptiles, amphibians, and other vertebrates populated the land. By its close, early dinosaurs and mammals had appeared, but a sparse fossil record has left scientists with few clues about what happened in between.

In contrast, the newly discovered fossils provide a virtual "Who's Who" of the Middle-Late Triassic animals in Madagascar. To begin with, the research team found two new dinosaurs that appear to be older than Herrerasaurus and Eoraptor, the current record-holders for dinosaur seniority. The new dinosaurs were prosauropods, herbivores with small heads and long necks that could walk on two or four legs. These primitive dinosaurs either shared a common ancestor with, or were themselves ancestors to, the mighty sauropod dinosaurs that evolved later, such as Apatosaurus. The scientists plan to hold off on formally naming their new finds until more of the prosauropods' remains are cleaned or excavated.

The fossils were discovered by John Flynn, of the Field Museum in Chicago, J. Michael Parrish, of Northern Illinois University, Berthe Rakotosamimanana, of the Université d'Antananarivo in Madagascar, William Simpson of the Field Museum, and Robin Whatley and André Wyss, of the University of California at Santa Barbara.

"The fossils are exquisitely preserved. They show a level of detail far superior to everything else from that time," said Flynn. Thus far, the team has excavated a selection of jaws and expects to round out the collection with more fossils that are currently being removed from the sediments they are encased in.

Flynn and his colleagues also found fossils from several other vertebrates the same age as the two new prosauropods. These include three members of the branch of animals that includes modern day reptiles and five members of the branch that includes mammals. Most of the eight animals have never been seen before, and one of the so-called "mammal-like reptiles" is described in more detail, together with the two prosauropods, in this issue of Science.

Several of the animal lineages were thought to have died out by the time dinosaurs appeared. So when Flynn and his colleagues found evidence that the two groups coexisted, they knew it could mean one of two things. Either these animal fossils were unusually young, or the dinosaur fossils were unusually old. Previously, radioisotope dating had shown the oldest known dinosaurs, Herrerasaurus and Eoraptor, to be just under 228 million years old. Could the new prosauropods be even older?

Because the rock layers at the Madagascar sites have not yet yielded the right minerals for radioisotope dating, Flynn and his colleagues had to use other clues from the fossil record to determine the age of their finds. Judging from the anatomical details of the fossils, two of the animals (one a parrot beaked reptile, the other an early relative of mammals) appear to be more primitive cousins to similar animals already known to be about 228 million years old. Also, the Madagascar record is suspiciously lacking in fossils of aetosaurs, small, armored reptilian herbivores that were abundant about 228 million years ago. Flynn and his colleagues have therefore concluded that their find is more ancient (probably closer to 230 million years old) making the two new prosauropods the oldest dinosaurs ever discovered.

The five pre-mammalian animals that the researchers discovered should also shed much-needed light on the currently murky picture of the origins of the first true mammals. For example, an essential question is how this line of large, cold-blooded "mammal-like reptiles" evolved into small warm blooded mammals, many of which then evolved to much larger sizes once again, following the extinction of the dinosaurs. "The new fossils will help us tease that evolutionary transformation apart," said Flynn.

The paleontologists also expect that their find will provide clues as to how the breakup of the supercontinent Pangaea, which began in the Triassic, affected the course of evolution.

"There were critical evolutionary events occurring in the Triassic, in response to climate changes and the beginning of the break-up of the supercontinent Pangaea, but we haven't had a good record of them until now," said Flynn.
-end-
ORDER ARTICLE #21: "A Triassic Fauna from Madagascar, Including Early Dinosaurs," by J. J. Flynn and W. F. Simpson at the Field Museum in Chicago, IL; J. M. Parrish at Northern Illinois U. in DeKalb, IL; B. Rakotosamimanana at U. d'Antananarivo in Antananarivo, Madagascar; R. L. Whatley and A. R. Wyss at U. of California in Santa Barbara, CA. CONTACT: To schedule an interview with John J. Flynn please contact Nancy O'Shea or Patricia Kremer in the Field Museum Communications Office at 312-665-7100 (phone)

For copies of this article please call 202-326-6440 or email scipak@aaas.org. For visuals or related materials please contact Nancy O'Shea or Pat Kremer in the Field Museum Communications Office at 312-665-7100 (phone).



American Association for the Advancement of Science

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